The present invention relates generally to the release of silicone pressure sensitive adhesives, herein called SPSAs. In a particular aspect, this invention relates to curable coating compositions and to articles of manufacturing comprising the cured coatings.
SPSAs, such as those disclosed in U.S. Pat. Nos. 2,736,721; 2,814,601; 2,857,356; 3,528,940; 3,929,704; 3,983,298; 4,309,520; Canadian Patent No. 711,756 and British Patent No. 998,232 are well known for their excellent thermal stability and tenacious adhesiveness. While these properties are valuable, the adhesiveness, e.g., tack and/or adhesive strength, of SPSAs presents a significant problem. Whether the SPSA is in the form of roll of tape, an adhesive layer on an article protected with a peelable backing, or a transfer adhesive layer protected on two surfaces by peelable backings, the SPSA must be separated from an adjacent surface provided with a release layer before it can be used for its intended purpose. Because of its tenacious adhesiveness specially designed release coatings are required for SPSA's.
Conventional release films which have been used with organic pressure sensitive adhesives (OPSAs) are generally unsuitable for use with SPSAs for a number of reasons. They may provide too tight release, i.e., too much force (the release force) may be required to remove the adhesive coated substrate from the release surface and in an extreme case the adhesive coated substrate may tear; they may not be sufficiently cohesive, e.g., the release coat may be displaced by the adhesive and transfer to the adhesive surface thereby reducing adhesive effectiveness; or when the SPSA is cast directly on the release backing the release film may provide unacceptably tight release or the SPSA may be contaminated with the release agent.
One class of release backing which has been found to be suitable for use with SPSA's employs fluorosilicone polymers. Examples of this type of backing are provided in U.S. Pat. Nos. 5,132,366; 4,980,443; 4,968,766; 4,889,753; 4,842,902; 4,736,048. This system has been found to suffer from several drawbacks which limit its usefulness. There is often a need to adjust the release properties of a backing and it is very difficult to do this using the fluorosilicone system because the perfluoro monomer is reacted into the fluorosilicone polymer off-site. Thus, the system has a fixed fluorine content which determines the release force and it is difficult to control the release properties of the coating and thereby tailor its release properties to the particular needs of the particular adhesive system with which the polymer is used. In addition, the fluorosilicone polymers are comparatively expensive which makes the release coating undesirable for use on paper or highly textured or absorbent substrates. From a practical standpoint, this limits the economic usefulness of the coating to application to films.
Release coatings which contain polymers including perfluoro groups are known in the art. For example, U.S. Pat. No. 4,523,059 to Dabroski discloses aqueous release coating compositions containing polymers derived from perfluoroalkylalkyl acrylates. U.S. Pat. No. 4,873,140 to Mcintyre discloses a coating of an in situ polymerized poly(perfluoropropylenoxy) acrylate or methacrylate. U.S. Pat. No. 4,472,480 to Olson discloses a perfluoropolyether release coating. U.S. Pat. No. 3,536,749 to Grones discloses an acrylate adduct of a fluorocarbon amide.
U.S. Pat. No. 3,502,497 to Crocker discloses a release coating comprising a copolymer of stearyl methacrylate and acrylonitrile, a release agent, and a film forming composition based upon an alkyd resin.
An improved release backing for pressure sensitive adhesives (PSAs), and particularly, SPSAs is thus needed in the adhesive industry.